The present invention relates generally to an endless abrasive belt surface treating appratus, more specifically a cross-belt sanding machine having an improved platen arrangement for such an apparatus. The apparatus includes means for orbitally driving the platen along with the work-contacting portion of the abrasive cross-belt in or along an oscillatory or epicyclic path whle work is being carried or conveyed through the machine and being treated by the sanding belt. Specifically, the improved cross-belt sander of the present invention employs an oscillating platen, with the nature and contact motion between the abrasive cross-belt surface and the surface of the work being controlled by the conventional drive motion of the belt, and additionally by the oscillatory motion of the platen.
The present invention constitutes an improvement over that certain arrangement disclosed and claimed in my co-pending application Ser. No. 643,701, filed Aug. 24, 1984, entitled "Wide Belt Sanding Machine with Platen Oscillating Means", and assigned to the same assignee as the present invention, the substance of which is incorporated herein by reference. By way of contrast, the present arrangement relates to a cross-belt sanding machine rather than a wide belt sanding apparatus, while utilizing certain features of the oscillating platen system of application Ser. No. 643,701.
Belt sanders utilizing stationary platens are known in the prior art, with one such system being disclosed in U.S. Pat. No. 3,832,807, Kiser et al,, assigned to the same assignee as the present invention. Cross-belt sanders are also well known, including their basic structural framework along with their basic drum or rollr mounting means.
In a typical cross-belt sanding machine, there is provided a platen base forming a sanding head and with an endless abrasive belt trained over a plurality of rollers or drums, at least one of which is power driven, the balance of the rollers being idlers and/or guides for the belt as it moves through its orbit. The platen is normally interposed between a pair of belt guiding rollers which serve to define the belt orbit.
In the present arrangement, the belt is driven along a generally rectangular orbit or path, with the drive roller or drum preferably being disposed at one upper corner zone of the belt orbit. A sufficient amount of wrap is provided on the drive roller for it to accomplish its drive function, and with added rollers or drums being disposed closely adjacent to and on either side of the platen normally being idlers and adapted to move in an orbital path with the platen per se.
In the cross-belt sanding machine of the present invention, it has been found that the addition of the orbital platen provides for improved performance in a number of ways. For example, the utilization of this arrangement provides for improved belt life over that obtained with stationary platens, and with significantly less surface wear being observed on the belt. Additionally, improved properties are obtained in the workpieces, including improved surface qualities. Also, it has been found that it is possible to use a coarser grit on the abrasive cross-belt, with greater belt speds being possible and useful without sacrificing or reducing the surface quality of the finished product. Accordingly, belt life as well as production rates are improved without sacrificing or causing any deterioration of quality of the work product. Either a single cross-belt, or two tandemly arranged cross-belt systems may be utilized for the operation.
Typically, in the present device, work is fed into the machine by a feed system or conveyor assembly that comprises an endless horizontally oriented conveyor belt, the upper span or flight of which may cooperate with one or more pinch-rolls so as to grip the work and feed it through the machine at a uniform rate, and in a predetermined angular direction relative to the abrasive belt and its direction of travel. Alternatively, and in lieu of pinch-rolls, stationary edge guides or fences may be employed. During a typical sanding operation, of course, the top surface of the work is arranged in contact with the working surface of the abrasive cross-belt. In order to accommodate and adapt the apparatus of the present invention to workpieces having different thicknesses, the conveyor assembly is adjustable either upwardly or downwardly toward or away from the plane of the cross-belt platen, the assembly normally being supported against the force or thrust of work arranged on the conveyor belt. When two cross-belt head assemblies are arranged in tandem, it is normally desirable to provide for horizontal adjustment of at least one of the platen surfaces, relative to the other, in order to accommodate stock removal accomplished through exposure to the first cross-belt assembly.
In the utilization of a cross-belt sanding apparatus with an orbital platen, vibrational forces generated by the apparatus are generally quite low, particularly when arranged according to the present invention. This is believed to be due to the feature of the belt direction being generally transverse to the direction of motion of the work, while other factors may contribute to this reduction as well.
Belt sanding apparatus with vertically adjustable conveyors are disclosed in U.S. Pat. No. 3,832,807 referred to hereinabove, and reference is made to the disclosure in that patent for the details of the adjustable conveyor design.